The number of bacteria in a petri dish increased by 20 percent…

The number of bacteria in a petri dish increased by 20 percent every 2 hours. If there were 72 million bacteria in the dish at 6: 00 p.m., at what time were there 50 million bacteria in the dish?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #71829